Referring to FIGS. 1A and 1B, conventional magnetic elements, such as transformers or inductance elements, include a first magnetic core 11 and a second magnetic core 12. The first magnetic core 11 has a central post 111, and the second magnetic core has a central post 121. A single air gap 14 is formed between the central post 111 and the central post 121 to prevent magnetic saturation. However, when such a single air gap 14 is larger, higher magnetic leakage may occur and thus increase energy loss. In addition, a winding 13 is fixed between the first magnetic core 11 and the second magnetic core 12 through a winding frame 10. The winding frame 10 occupies a considerable space and thus reduces the total number of windings between the first magnetic core 11 and the second magnetic core 12 so that utilization ratio of the winding and working efficiency of the magnetic element are reduced. Another conventional magnetic element includes several air gaps formed on a central post is seen in the market. The multiple air gaps can reduce and disperse magnetic leakage loss and therefore decrease magnetic flux diffusion. However, the central post limits the amount and distribution of the air gaps. When the number of the air gaps in the central post is increased, a distance between two adjacent air gaps is reduced. When the distance between two adjacent air gaps is less than a critical value, the magnetic flux diffusion cannot be further effectively reduced, and the improvement for the working efficiency is therefore limited.